Finding opening and closing price using sqlite GROUP BY statement (accessing main query alias in subquery)

I want to preface this post by saying that I am a SQL(ite) newbie. My main goal is to find the opening/closing/high/low/average prices of each 5 minute interval of these stock prices. I can get the high/low working with min/max and the group by query but I am running into problems with the opening/closing. My database looks something like this

SYMBOL | DATETIME           |PRICE
AAPL   | 1999-06-01 09:30:01|45.0
AAPL   | 1999-06-01 09:30:03|44.9375
AAPL   | 1999-06-01 09:30:04|44.9375
AAPL   | 1999-06-01 09:30:05|44.9375
AAPL   | 1999-06-01 09:30:06|44.9375
AAPL   | 1999-06-01 09:30:07|45.0
AAPL   | 1999-06-01 09:30:08|45.0
AAPL   | 1999-06-01 09:30:09|44.9375
AAPL   | 1999-06-01 09:30:11|45.0
AAPL   | 1999-06-01 09:30:12|44.96875

The following query

SELECT SYMBOL, MIN(DATETIME) AS MINDT, MAX(DATETIME) AS MAXDT, AVG(PRICE)
FROM stocks
WHERE DATETIME < '1999-06-02 00:00:00'
GROUP BY strftime('%s', DATETIME)/(60*5) LIMIT 4;

results in

AAPL|1999-06-01 09:30:01|1999-06-01 09:34:41|44.9269724822695
AAPL|1999-06-01 09:35:22|1999-06-01 09:39:58|44.8615196078431
AAPL|1999-06-01 09:40:03|1999-06-01 09:44:58|44.9800531914894
AAPL|1999-06-01 09:45:05|1999-06-01 09:49:52|44.9397321428571

whereas

SELECT SYMBOL, MIN(DATETIME) AS MINDT, MAX(DATETIME) AS MAXDT, AVG(PRICE),
(SELECT PRICE FROM stocks WHERE DATETIME=MINDT),
(SELECT PRICE FROM stocks WHERE DATETIME=MAXDT)
FROM stocks
WHERE DATETIME < '1999-06-02 00:00:00'
GROUP BY strftime('%s', DATETIME)/(60*5);

throws this error in SQL

Error: near "MINDT": syntax error

and in R

Error in sqliteSendQuery(con, statement, bind.data) : 
  error in statement: no such column: MINDT

I have googled around and I think I found what is wrong with my query: you can not acces an alias made in main query in a sub query (i.e. reference MINDT in the subquery). But my I lack SQL knowledge to find a fix to this. Is there anyone that could help me out here?