What is the most likely diagnosis of a 2-week-old neonate presenting with vomiting, weight loss, circulatory collapse, and enlarged penis with a pigmented scrotum?

The presentation of the 2-week-old neonate in the scenario aligns well with congenital adrenal hyperplasia (CAH), particularly the classic form caused by 21-hydroxylase deficiency. This condition leads to inadequate production of cortisol and aldosterone due to enzyme blockages in the adrenal steroid synthesis pathway, resulting in an overproduction of adrenal androgens.

The key symptoms presented in the neonate's case include vomiting, weight loss, circulatory collapse, and the enlarged penis with a pigmented scrotum. These features suggest that there is an excess of adrenal androgens, which can cause masculinization in male infants, hence the enlarged penis and pigmented scrotum. The vomiting and weight loss are indicative of dehydration and adrenal crisis, often seen in untreated CAH due to the loss of aldosterone, leading to electrolyte imbalances and hypovolemia.

In this context, congenital adrenal hyperplasia is the most likely diagnosis as it comprehensively explains the signs and symptoms presented. Other potential conditions listed do not account for the specific combination of symptoms, particularly the sexual development features associated with CAH.